When you begin creating a bottom-up mesh, the first requirement is to define the domain in which the mesh will be created. The domain determines whether the bottom-up mesh is created as a native mesh or as a collection of orphan nodes and elements. To create a native mesh, you choose a three-dimensional geometric model region that has been assigned the bottom-up meshing technique in the Mesh Controls dialog box. (For more information, see “Assigning mesh controls,” Section 17.18.1.) If there are no geometric regions with the bottom-up technique assigned, you must create one or use the orphan element domain.

Selecting a three-dimensional region as the domain also indicates that you intend to fully associate the bottom-up mesh with geometry. The association between mesh and geometry is necessary to transfer loads, boundary conditions, and other information from the geometry to the mesh. Mesh-geometry association is discussed in “Mesh-geometry association,” Section 17.12.

Selecting orphan elements as the domain indicates that the bottom-up mesh will not be fully associated with geometry. The created elements may either have no association with geometry, or you may associate the created orphan mesh entities with adjacent geometric faces. Associating the orphan mesh faces with adjacent geometric faces allows Abaqus/CAE to create a compatible mesh when you mesh the geometry.